The need for positional accuracy when mounting components on electrodes formed on a board has been becoming ever more stringent as electronic components become smaller and mounting density becomes higher. For example, micro-components of only about 0.6 mm×0.3 mm in size are already commercialized. These small components require extremely accurate mounting positions. The electrode position has conventionally been confirmed by identifying a recognition mark provided on the board to ensure correct positioning of a component onto an electrode when the component is placed on the electrode on the board by means of a transfer head.
However, micro-components as described above may show defects after being mounted due to lack of mounting position accuracy for the reasons described below.
A conventional method for mounting micro-components is described next with reference to drawings.
FIGS. 5A to 5C are process charts of the conventional component mounting method.
In FIG. 5A, numerous electrodes 1a onto which electronic components are soldered are provided on board 1. Solder paste S is printed on electrodes 1a before the mounting process. In the mounting process, the position of each electrode 1a is identified based on mounting position data by detecting recognition mark 1b provided at the corner of board 1. Component 2 is then mounted on identified electrode 1a. 
However, the position of solder paste S printed on electrode 1a does not completely coincide with the position of electrode 1a due to changes of shape with time in board 1 or screen mask, and a slight positional deviation d may occur as shown in FIG. 5A. If component 2 is placed in relation to the position of electrode 1a in this state, as described above, the center line of a terminal of component 2 will deviate with respect to solder paste S as shown in FIG. 5B.
If board 1 is heated in a reflow process in this state, component 2 may rotate in the direction shown by an arrow in FIG. 5C as solder paste S melts. The rotation occurs due to non-uniform distribution of solder paste S contacting component 2 with respect to the center line of the terminal of component 2. In other words, component 2 rotates in the soldering process because the force of attraction generated by surface tension is applied to component 2 when melted solder wets and spreads on the terminal surface, and this force is applied asymmetrical with respect to the center line of component 2. Positional deviation in the direction of the arrow remains if solder paste S solidifies in this state, resulting in defective mounting. Accordingly, the conventional component mounting method may cause defective mounting due to positional deviation occurring at the time of solder printing.